Recovery of tar acids



May 3l, 1938. J. 3` HATMAN '2,119,132v

RECOVERY OF TAR ACIDS Filed April 15, 1935 Patented May 31, 1938 UNITEDSTATES ArsN'r OFFICE RECOVERY or TAR ACIDS Application April 13, 1935,Serial No. 16,240'

8 Claims.

This invention relates tothe art of recovering tar acids from tar andparticularly to a process by which the tar acids may be separated in asimple, economical manner from the tar produced incidental to themanufacture of coke. An arrangement of apparatus that it has been foundadvantageous to use in the performance of the new process is also a partof this invention.

In accordance with the usual process of manufacturing coke, a. quantityof tarry material results as a by-product. This tarry material, or crudetar as it will hereafter be called, has a specic gravity of around 1.06to 1.18 and ordinarily contains from 21/2 to 6% of tar acids and up toabout 10% of water. The tar acids, which consist mainly of phenol andits homologues, such as the cresols and xylenols, are valuablecommercially but are quite dilicult to isolate according to knownprocedures.

The practice heretofore has usually been to dehydrate the crude tareither by evaporating off the water or centrifuging. After dehydrating,the crude tar is distilled in a tar still and separated into twofractions, the fraction boiling below 270 C. being known as tar oil andthe remainder simply as tar, or as tar residue. The tar acids aresubstantially wholly contained in the tar oil and are present thereinina concentration of between and 25%.

This tar oil fraction is subjected to further treatment to separatethese acids. Such treatment ordinarily consists in intermixing the taroil with an aqueous caustic soda solution of a concentration suilcientto convert the tar acids into phenolates, cresolates and the like. Thesecompounds, which will hereafter be referred to generally as phenolates,dissolve readily in the caustic solution and are subsequently separatedfrom the tar oil by allowing the mixture to settle into an aqueous layerand an oil layer and then decanting. The aqueous solution so obtained isthereafter treated by blowing carbon dioxide gas through it, or may betreated with an acid, usually sulphuric, to convert the dissolvedcompounds back into tar acids. The tar acids, being insoluble, arethereafter separated from the resulting solution of sodium carbonate orsodium sulphate by gravity settling.

The difficulty with such a process is that it requires a dehydrationand. distillation of the heavy tarry material which is difcult andtroublesome and which many coke plants are not equipped to accomplish.Hence the tar must often be sold without extracting the tar acidstherefrom, to refineries especially equipped for this work and theserefineries must be equipped to carry out the relatively long andinvolved process outlined above.

The present process has been conceived to overcome difficulties involvedin the practice of the process now in use and to produce relatively puretar acids simply and expeditiously, directly from the original tarrymaterial as it is produced by the coke plant. According to anapplication Serial No. 754,718, filed by Charles M. 10 Ambler, Jr.and-Charles E. Underwood on November 26, 1934 which has matured intoPatent #2,081,692, it has been found that if this original tarrymaterial is mixed directly with a basic solution such as an aqueoussolution of caustic 15 soda or caustic potash, capable of converting thetar acids into the corresponding phenolates, and thereafter separatedfrom such solution with sufcient promptness to avoid emulsiondifficulties, such separation can be effected and the separated solutionwill contain substantially all of the tar acids in the form of solublephenolates. These compounds may thereafter be reconverted into tar acidsby the addition of acid, and separated.

The present invention is an improvement upon the process and apparatusdescribed in the Ambler et al. application and provides a modifiedprocess according to which the aqueous solution of phenolates formed bythe action of water and caustic soda upon the tar, is recycled until theconcentration of phenolates therein isv greatly increased and-'theeii'ciency with which these phenolates may be separated from the aqueoussolution is materially bettered. Furthermore, the g5 present inventionprovides a system of apparatus by which this novel process may beperformed either continuously or by the batch. Further details that addto the efciency or desirability of the new process and apparatus willappear more A fully from a consideration of the following detaileddescription of the preferred mode of practicing the invention and of thesystem of apparatus which has been found especially adapted for theperformance of this process.

In the drawing, forming a part of this application, the new process andsystem of apparatus for performing it are illustrated in their preferredform by a flow sheet. According to this ilow sheet the original rawmaterials are water, tar, caustic soda solution and stack gas from thecoke ovens. In place of at least part of the water, after the processhas been started in operation, a solution of phenolates from previouslyextracted tar is supplied.

According to illustrated process, a caustic soda solution, usually of aconcentration of about 8% by weight is supplied to the mixer through aconstant head pump and a proportioningfmeter in approximately the ratioof one gallon of caustic solution to each iive or six gallons of tar,the tar also being fed through a constant head pump and theproportioning meter. At the same time an aqueous liquid, either Water orphenolate solution from a previous extraction or a mixture of the two,is fed through another` constant head pump and the proportioning meterinto the mixer. The aqueous liquid may either enter the mixer with thecaustic solution and the tar or may be supplied to theseconstituentsafter they have been partially mixed, in accordance with the processdescribed in the above mentioned application. The ratio of the aqueousliquid to the tar is usually about 2 to l by volume but may be as low as1 to 1. The ratio of caustic solution to tar is preferably adjusted sothat approximately 1.4 pounds of caustic soda are added for every gallonof tar acids in the tar.

After the mixing has been completed, preferably in the manner describedby the above mentioned application, although it may be done in any othermanner found convenient, the mixture is brought to a temperature ofaround 80 C. and centrifuged to separate the tar from the aqueoussolution of phenolates formed by the reaction of the caustic sodasolution upon the tar acids in the tar.

The resulting aqueous solution of phenolates is passed into a storagetank from which it may be returned by a pump and be recycled through thesame process. As this recycling is continued the supply of water to thesystem may be d iminished or stopped altogether, with the result thatthe concentration of phenolates in the solution increases until aconcentration is reached at which the phenolate solution contains asufficient percentage of phenolates to enable their recovery to beefliciently made. At that time the whole of the phenolate solution maybe directed into other apparatus for recovering the tar acids therefrom,or a portion of the phenolates may be directed into such apparatus andthe remainder recycled to collect more tar acids. The concentration ofphenolates in the solution will not increase indefinitely, for thecaustic soda solution added tends to dilute the phenolate solution andthus to reduce the concentration and in addition a certain amount ofwater is extracted from the tar itself. Usually there is around six toten percent of water in the tar as it is originally received and of thisall but about 0.5 to 1.5 percent is extracted and passes into thephenolate solution.

As the phenolate solution is recycled, the addition of caustic sodasolution may be discontinued, if desired, and sufficient caustic soda,in solid form, added to the phenolate solution to maintain the desiredconcentration. Alternatively the addition of the caustic soda solutionmay be continued and the rate of addition adjusted to maintain theproper concentration, namely, around 1.4 pounds ofcaustic soda pergallon of tar.- Y

If an amount of phenolate solution equal to the amount of caustic addedplus the amount of water extracted from the tar, is removed to therecovery apparatus continuously and no additional water is added, thesystem willreach an equilibrium point at which the concentration of thephenolates in the phenolate solution Will be substantially constant. Apoint of equilibrium will also be reached if water is added at adelinite rate with the recycled phenolate solution and a suflicientquantity of the phenolate solution is Withdrawn continuously to balancethis water, as well as the water taken from the tar and the causticsolution.

The phenolate solution taken from the above described section of thesystem passes through a pump and suitable heating apparatus which raisesits temperature to around 90 C. to a springing tower where it passescountercurrent to gas from coke oven stacks. In so doing the phenolatesolution absorbs carbon dioxide and the tar acids are re-formed. Some ofthe water and a portion of the tar acids are Volatilized and pass offthrough the top of the tower, but these are condensed in a suitablecondenser and passed to a settling tank together with the portion of thetar acids and water solution that remains liquid. In the settling tankthe re-formed tar acids separate from the aqueous solution of carbonatesformed in the springing tower. The carbonate solution is passed tosuitable apparatus where it is regenerated into caustic soda bytreatment with lime.

The tar acids, which still contain some residue and some Water aredistilled to obtain three portions, residue, dry tar acids and a mixtureof tar acids and water. The residue is discarded, and the tar acid andwater mixture permitted to settle. Upon settling a quantity of water isrecovered which may be discarded or added back to the phenolate solutionbeing recycled. There remains crude tar acids which together with thetar acids recovered directly from the distillation, may be treated inany suitable manner to further refine them or to separate them into theindividual tar acids.

While the process and system of apparatus described above are thepreferred form, it is to be understood that considerable modificationsmay be made in both the process and the apparatus without departing fromthe principles of this invention. For example, any suitable device maybe substituted for the constant head pumps and the proportioning meter,for feeding accurately-proportioned amountsrof caustic soda solution,tar and phenolate solution or water to the mixer, The phenolate solutionor Water may be added at any time during the mixing and the constituentsmay be heated either before or after mixing to a temperature of around80 C., or the process may be performed without the application of heatto the constituents prior to the centrifuging. Also, although it isdefinitely preferred to use a centrifuge to separate the phenolatesolution from the tar, other means of separation, such as gravity orfiltration may conceivably be employed.

As has already been indicated, the phenolate solution resulting from thetreat-ment is recycled either in whole or in part and this recycling maybe carried out to any desired extent, thus building up a concentrationof phenolates in the solution of anywhere from 5 to 40% or even greater.Preferably, in order to make the process economical, the concentrationis built up to at least or 20% and may be much higher. 1f the process isto be performed by the batch, all ofthe phenolate solution or at least amajor part of it will ordinarily be drawn off at one time, whereas ifthe process is to be performed continuously a smaller portion, usuallyfrom 5 to 15%, by volume will be removed to the recovery apparatuscontinuously.

In the recovery of the tar acids from the phenolate solution the stepsand the apparatus may also be modied. Thus, the phenolate solution maybe passed to the springing tower without previous heating or thephenolate solution may be treated with sulphuric acid instead of stackgas to liberate the tar acids. If desired, the tar acids may be takendirectly from the rst settling tank without any further distillation andused in this condition or passed to other apparatus for puriiication.

I claim:

l. A process of removing tar acids from tar that comprises separatelymixing with the tar a constant proportion of an aqueous caustic sodasolution and a constant proportion of water, centrifuging the resultingmixture to remove the tar, recycling the aqueous liquid recovered fromthe centrifuge by mixing it with additional tar and recovering the taracids from the recycled aqueous liquid.

2. A process of removing tar acids from tar that comprises separatelymixing with the tar a constant proportion of an aqueous caustic sodasolution and a constant proportion of water, centrifuging the resultingmixture to remove the tar, recycling the aqueous liquid recovered fromthe centrifuge by mixing it with additional tar and additional causticsoda solution, and recovering the tar acids from the recycled aqueousliquid.

3. A process of removing tar acids from tar that comprises mixing withthe tar a constant proportion of caustic soda and a constant proportionof Water, centrifuging the resulting mixture to remove the tar,recycling the aqueous liquid recovered from the centrifuge a pluralityof times by mixing it with additional tar and recovering the tar acidsfrom the recycled aqueous liquid.

4. A process of removing tar acids from tar that comprises separatelymixing with the tar a constant proportion of an aqueous caustic sodasolution and a constant proportion of water, heating the mixture toaround C., centrifuging the resulting mixture to remove the tar,recycling the aqueous liquid recovered from the centrifuge a pluralityof times by mixing it with additional tar and additional caustic sodasolution, and recovering the tar acids from the recycled aqueous liquid.

5. A continuous process for the removal of tar acids from tar thatcomprises continuously and separately mixing with tar an aqueous causticsoda solution and water in predetermined proportions, heating themixture to around 80 C., continuously centrifuging to separate themixture so formed into a tarry and an aqueous phase,

' continuously returning a portion of the aqueous phase to the processto be mixed with the tar; and continuously withdrawing a portion of theaqueous phase and recovering tar acids therefrom.

6. A process for the recovery of tar acids from tar that comprisesmixing with tar an aqueous caustic soda solution containing about 8%caustic soda by weight and in such proportion that approximately 1.4pounds of caustic soda are added for each gallon of tar acids in thetar, mixing with these two constituents water in the proportion ofapproximately two gallons of the aqueous liquid to each gallon of tar,heating the mixture to approximately 80 C., centrifuging to resolve themixture into a tarry portion and an aqueous portion, recycling theaqueous portion as at least a part of the aqueous liquid added to thetar and caustic soda solution, and thereafter passing the said aqueousportion into contact with a gas containing carbon dioxide whereby thetar acids are precipitated therefrom, settling to separate the tar acidsfrom the aqueous solution and distilling the tar acids so separated.

'7. A continuous process for the removal of tar acids from crudeundistilled tar having a speciiic gravity in excess of 1.06 thatcomprises continuously mixing the crude tar with an aqueous alkalinesolutionv to convert the tar acid content of said crude tar into thecorresponding salts of said tar acids, passing the mixture of crude tarand the aqueous solution of said salts formed by a reaction of thealkaline solution with said tar acids continuously through a centrifugalseparator and thereby separating the mixture into a tarry and an aqueousphase, continuously returning a portion of the aqueous phase separatedfrom the centrifugal separator into confluence with alkali and a furtherquantity of said crude tar and continuously withdrawing a portion of theaqueous phase and recovering tar acids therefrom.

8. A process for the removal of tar acids from crude undistilled tarhaving a specic gravity in excess of 1.06 that comprises mixing thecrude tar with an aqueous alkaline solution to convert the tar acidcontent of said crude tar into the corresponding salts of said taracids, passing the mixture of crude tar and the aqueous solution of saidsalts formed by a reaction of the alkaline solution with said tar acidsthrough a centrifugal separator and thereby separating the mixture intoa tarry and an aqueous phase, returning a portion of the aqueous phaseseparated from the centrifugal separator into confluence with alkali anda further quantity of said crude tar and withdrawing a portion of theaqueous phase and recovering tar acids therefrom.

JULIUS GEORGE HATMAN.

